Image reading apparatus having a blast mechanism

ABSTRACT

A blast mechanism in an image reading apparatus reliably cools heat generated in boards by a blast path with high cooling action among a plurality of boards disposed inside a casing. A partition plate is disposed between a plurality of boards disposed at a distance away in a layered shape, a first blast path is formed between a top of the casing and a first board, a second blast path is formed between the first board and the partition plate, a third blast path is formed between the partition plate and a second board, and a flow of cooling air is formed in each blast path with a blast fan. A blast mechanism for sending cooling air includes the casing, first and second boards disposed vertically inside the casing, the partition plate disposed between the first board and the second board, and fans for sending cooling air.

TECHNICAL FIELD

The present invention relates to improvements in a cooling mechanism for sending outside air from an air inlet of a casing to a heat-producing board disposed inside the casing to cool in an image reading apparatus.

BACKGROUND ART

This type of apparatus has widely been known as an apparatus which has a platen to place an original document image in an apparatus casing, and guides reflected light of light applied from a light source to an imaging device by a reading optical system to perform photoelectric conversion.

Then, inside the casing are disposed a plurality of boards such as a power supply board for supplying power to a light source lamp, a sensor board for controlling a photoelectric converter, a control board for controlling scanning operation of image reading, and an image processing board for performing signal processing on read data. Then, these boards are disposed, while being stacked in a layered shape inside the casing.

For example, in Patent Document 1, a plurality of boards is disposed inside a casing, while being spaced a distance apart, and a cooling fan is disposed in each board to form a flow of cooling air from one end to the other end. In the Document, cooling air is sent to a heat sink integrally attached to the board.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Patent Application Publication No. 2004-88023

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

The above-mentioned method is known in various kinds of apparatuses in which a plurality of boards is disposed at a distance away in the layered shape and cooling air is sent to each board. In this case, Patent Document 1 and the like also propose that a heat sink is integrally provided in the board, and that a flow of cooling air is formed in a direction of a fin formed in the heat sink.

Conventionally, in arranging a plurality of boards in the layered shape, in order for generated heat not to affect the other boards, the boards have been disposed at relatively wide distances away. Therefore, even when a flow of cooling air is formed with a blast fan from an air inlet to an air outlet of the casing, the flow of air is changed to a turbulent flow in a position relatively near the blast fan of the board, and there is a problem that the air does sufficiently not reach a position spaced apart from the blast fan of the board.

The problem is caused by that airtightness (sealing degree) of the casing is not maintained, air thereby flows onto the board surface from every direction, and that the flow of cooling air is disturbed, while being also affected by parts mounted on the board.

It is an object of the present invention to provide a blast mechanism in an image reading apparatus for reliably cooling heat generated in boards by forming a blast path with high cooling action among a plurality of boards disposed inside a casing, without affecting the other board.

Means for Solving the Problem

To attain the above-mentioned object, in the present invention, a partition plate is disposed between a plurality of boards disposed at a distance away in a layered shape, a first blast path is formed between a top of a casing and a first board, a second blast path is formed between the first board and the partition plate, a third blast path is formed between the partition plate and a second board, and a flow of cooling air is formed in each blast path with a blast fan.

The invention is a blast mechanism for sending cooling air to an inside of a casing of an image reading apparatus, and includes a casing 1, first and second boards 24, 25 disposed vertically inside the casing, a partition plate disposed between the first board and the second board, and fans 33, 43 for sending cooling air to the first and second boards.

The top of the casing, the first board, the partition plate and the second board are disposed in this order from above, while being spaced a distance apart, the first blast path is formed between the top and the first board, the second blast path is formed between the first board and the partition plate, and the third blast path is formed between the partition plate and the second board. Then, each of the blast fans is disposed in a position for forming a flow of cooling air in the respective blast path.

By this means, in the first and second boards disposed vertically, flows of cooling air are formed between the partition plate and the first board, and between the partition plate and the second board. As compared with a turbulent flow occurring by concavities and convexities of placement parts and the like on the boards, the cooling air flowing along the partition plate is a laminar flow with little disturbance, and sends heat to outside the casing from an air inlet to an air outlet. Accordingly, it is possible to send air to a position spaced apart from the blast fan with simplified structure, and it is possible to obtain the cooling mechanism with a high cooling effect.

In the invention, the gap between the top and the first board is set wider than the gap between the first board and the partition plate. Then, an air volume of the first blast path is set at a capacity higher than an air volume of the second blast path.

By this means, a cooling flow with a wide distance is formed above the first board, a cooling air flow with a narrow distance is formed under the board, the upper cooling flow radiates heat by convention, and the lower cooling flow transports heat to the outside by a high velocity laminar flow.

In the invention, the partition plate is formed of a material with thermal conductivity higher than that of the first board. By this means, the partition plate forms a laminar flow with a relatively high velocity, and concurrently radiates heat propagated from the board.

In the invention, the blast fan is attached to a bracket fixed to the casing, and the partition plate is integrally coupled to the bracket. By this means, the partition plate performs both the function as a barrier wall to form an air flow between the partition plate and the board, and the function as an attachment seat to attach the blast fan.

In the invention, vent holes from the blast fan are formed in the bracket. By this means, the bracket functioning as the attachment seat of the blast fan forms a ventilating duct.

In the invention, in the first board is formed a power supply circuit for supplying power to a light source lamp disposed inside the casing, and in the second board is formed a control circuit of an image reading section disposed inside the casing. By this means, the power supply board with a relatively high heating value is disposed in the upper portion, the control board with a relatively low heating value is disposed in the lower portion, and it is possible to reduce the effect exerted on the other board due to convection of heat.

In the invention, in the casing are disposed a placement platen of an image to read, a reading carriage of the image to read, a light source lamp mounted on the reading carriage, a power supply board for controlling supply of power to the light source lamp, and a control board for controlling reading operation of the reading carriage, the power supply board forms the first board, and the control board forms the second board.

By this means, it is possible to efficiently cool heat-producing boards in an apparatus for reading an image while scanning the image on the platen with the reading carriage.

Advantageous Effect of the Invention

The present invention is to provide the partition plate between the first and second boards disposed vertically, and form flows of cooling air between the partition plate and the first board and between the partition plate and the second board, and therefore, exhibits the following effects.

Since electronic parts are arranged to protrude on the board, a flow of cooling air is disturbed and becomes a turbulent flow, and release of heat is disrupted. In contrast thereto, by arranging the partition plate, a laminar flow without disturbance is formed between the board and the partition plate, and a smooth air flow is formed from a vent to a vent.

Accordingly, in the present invention, it is possible to effectively cool the inside of the casing by forming a smooth flow layer between the partition plate and the board with simplified structure, otherwise the cooling air becomes a turbulent flow and is clogged among a plurality of boards.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating the entire configuration of an image reading apparatus according to the present invention;

FIG. 2 is an explanatory view of principal part of the apparatus of FIG. 1;

FIG. 3 is a plan view illustrating an internal layout configuration of the apparatus of FIG. 1;

FIG. 4 is an explanatory view of internal structure of a reading carriage in the apparatus of FIG. 1;

FIG. 5 is an explanatory view of principal part, while being an explanatory view of blast paths in the apparatus of FIG. 1;

FIG. 6 is an explanatory view of a cooling mechanism of circuit boards in the apparatus of FIG. 1;

FIG. 7 is an explanatory view of cooling air flows of the circuit boards in the apparatus of FIG. 1; and

FIG. 8 is an explanatory view of the arrow direction of FIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will specifically be described below according to Embodiments shown in drawings. FIG. 1 is an appearance explanatory view of an image reading apparatus A according to the present invention, and is comprised of a casing 1, main platen 2, sub-platen 3 and feeder unit F.

In the casing 1 are disposed the above-mentioned main platen 2, sub-platen 3 and board storage section 5. In the board storage section 5 are disposed various kinds of boards described later, and the section 5 is provided with a hinge attachment section 6 of the feeder unit F. “5 a” shown in the figure denotes a top of the casing 1 positioned in the board storage section 5, “7” shown in the figure denotes a first air vent formed in the casing, “8” shown in the figure denotes a second air vent, and “9” shown in the figure denotes an air outlet.

Each of the board storage section 5, first and second air vents 7, 8 and air outlet 9 shown in the figure is formed on a side wall surface 1 r on the rear side of the casing 1. The air vent 7 (8) and the air outlet 9 are disposed at a distance in opposite end portions of the rear side wall surface 1 r.

[Casing Structure]

As the casing structure, the casing 1 is formed in the shape of a box with exterior side walls (front-side external wall 1 f, rear-side side wall 1 r, right-side wall 1 s and left-side wall 1 n), top (5 a, main platen 2), and bottom plate Bs. The inside of the casing 1 is provided with a barrier wall 23, and is partitioned into a carriage travel area Cr, and board placement area Br with the barrier wall 23.

The barrier wall 23 shown in the figure forms a partition wall in the sub-scanning direction to divide the inside of the apparatus into two. Further, the carriage travel area Cr is disposed on the apparatus front side, and the board placement area Br is disposed on the apparatus rear side. This is because of enabling operation for setting an original document image on the main platen 2 disposed in the carriage travel area Cr to be performed easily from the apparatus front side.

On the barrier wall 23, guide rails (forming a part of a guide member 22 described later) are integrally formed to guide a reading carriage 10 in the sub-scanning direction Ay. In other words, the barrier wall 23 also functions as a guide member (guide rail) to guide the reading carriage 10 in the sub-scanning direction, while concurrently dividing the inside of the casing into the carriage travel area Cr and the board placement area Br.

The carriage travel area Cr is formed of space (hereinafter, referred to as first housing) enclosed with the barrier wall 23, front-side external wall 1 f, right-side wall 1 s and left-side wall 1 n, and the main platen 2 and sub-platen 3 are disposed on the top surface. The reading carriage 10 described later is disposed in the main scanning direction inside the space, and the carriage reciprocates in the sub-scanning direction inside the area.

The board placement area Br is formed of space (hereinafter, referred to as second housing) enclosed with the barrier wall 23, rear-side side wall 1 r, right-side wall 1 s and left-side wall 1 n, and the top 5 a and hinge attachment section 6 are disposed on the top surface.

Cooling air (outside air) is supplied from outside the casing to the first and second housings Cr, Br thus partitioned into two (or, two or more) portions by the barrier wall 23. Therefore, the first air vent 7 and second air vent 8 are formed in the rear-side side wall 1 r of the casing 1. Then, a first blast path 30 is disposed between the first air vent 7 and the first housing (carriage travel area Cr), and a second blast path 40 is disposed between the second air vent 8 and the second housing (board placement area Br).

The main platen 2 is comprised of a transparent placement surface to set an image original document in a rest state, and the sub-platen 3 is comprised of a transparent exposure surface to read a shifting image original document fed from the feeder unit F at a constant velocity. In addition, instead of providing the sub-platen 3 particularly, it is also possible to adopt a configuration (one-platen mechanism) for reading a traveling original document with a part of the main platen 2.

The first air vent 7 and second air vent 8 are disposed in mutually adjacent positions, and the air outlet 9 is disposed in a position spaced a distance in the sub-scanning direction. Then, outside air sucked from the first air vent 7 and second air vent 8 is sent in the main scanning direction and the sub-scanning direction, and is discharged to the outside from the air outlet 9. By the flows of air, the inside of the housing is cooled.

Further, since the first air vent 7 and second air vent 8 are disposed in mutually adjacent positions, the air vents do not directly suck again the air, which is sucked from respective air vents, cools the inside of the casing, and is warmed in the inner portion to discharge to the outside, into the inside. Accordingly, both of the air vents are capable of efficiently sucking outside air.

FIGS. 2 and 3 illustrate a configuration of the inside of the casing. Inside the casing is incorporated an image reading mechanism 4 for reading an original document image (still image) set on the main platen 2 or a shifting original document (shifting image) traveling on the sub-platen 3 in a line sequential manner.

The image reading mechanism 4 is comprised of one of contact reading structure and reduction optical reading structure. The apparatus shown in the figure indicates the reduction optical system reading structure, and the structure will be described. The reading mechanism 4 is comprised of the reading carriage 10, light source lamps 11, reflecting mirrors 17, condenser lens 18 and photoelectric sensor 13.

The reading carriage 10 (hereinafter, referred to as “carriage”) is supported to be able to shift along a pair of guide members 22 (guide rails, guide rods and the like) disposed on the front-side external wall 1 f and the rear-side side wall 1 r of the casing 1. The carriage 10 reciprocates along the main platen 2, while concurrently shifting to positions between the main platen 2 and the sub-platen 3.

To the reading carriage 10 is coupled a travel tow member 20 such as a timing belt and wire, and the travel tow member 20 is supported by a rotating member 21 such as a pulley and wind-up roll. To this rotating member 21 is coupled a drive motor (not shown in the figure; hereinafter, referred to as “carriage motor”). The travel tow member (timing belt 20), rotating member (pulley 21) and carriage motor (stepping motor) in the apparatus shown in the figure are incorporated into the casing 1.

An internal structure of the carriage 10 will be described according to FIG. 4. Into the carriage 10 are incorporated the light source lamps 11 (a pair of LED lamps in the apparatus shown in the figure), reading optical system 12, and photoelectric converter 13. The carriage 10 is made of a heat-resistant resin, and lamp placement sections 11 x, 11 y, mirror fix section 14, lens fix section 15 and sensor board fix section 16 are integrally formed. The rod-shaped LED lamps (light source lamps) 11 are fixed to the lamp placement sections 11 x, 11 y, and are disposed to apply light to the original document on the platen. To the mirror fix section 14 are fixed the reflecting mirrors 17 (17 a, 17 b, 17 c, 17 d, 17 e) having predetermined lengths in the main scanning direction.

Each of the mirrors 17 a to 17 e reflects reflected light such that the light from the light source lamps 11 is applied to the original document image, and forms an imaging optical path with a predetermined length. In the lens fix section 15, the lens 18 (image formation lens) that condenses output light from the reflecting mirror 17 is attached to be adjustable in position. Further, a sensor board 19 is attached to the sensor board fix section 16, and the photoelectric sensor 13 (photoelectric converter; CCD) is mounted on the board and is disposed so that the light from the condenser lens 18 forms an image on the photoelectric sensor (line sensor) 13.

The light source lamps 11, imaging optical system 12 and photoelectric sensor 13 are arranged in the shape of a line so as to read the original document image in a line sequential manner. In other words, the photoelectric sensor 13 is a line sensor (CCD or the like), and the condenser lens 18 forms a line image on the line sensor. Therefore, the reflecting mirrors 17 and light source lamps 11 are configured to emit and reflect line light. Then, the carriage 10 shifts in the sub-scanning direction orthogonal to the main scanning direction of the photoelectric sensor (sensor alley) 13.

In addition, the Embodiment is described in which the photoelectric sensor 13 and condenser lens 18 are mounted on the carriage 10, and it is also possible to fix the imaging optical system to the bottom portion of the casing, for example, chassis. In this case, a transmission cable 26 described later is comprised of a power supply line 26 a and control line 26 b thereof.

[Board Structure]

The board storage section 5 is disposed inside the casing 1. The casing 1 shown in the figure is provided with the barrier wall 23 to partition the inside of the box-shaped casing into the carriage travel area (first housing) Cr and the board placement area (second housing) Br. The board storage section 5 is comprised of space enclosed with the barrier wall 23, the rear-side wall surface 1 r, top 5 a and bottom plate (chassis) Bs.

Further, in the carriage travel area (first housing) Cr partitioned by the barrier wall 23 is formed space enclosed with the barrier wall 23, front-side external wall 1 f, main platen 2, and bottom plate (chassis) Bs. Thus, by the barrier wall 23 are formed an air flow (sub-scanning direction blast path 40) to send air to the board placement area Br and an air flow (main scanning direction blast path 30) to send air to the carriage travel area Cr.

In the board storage section 5 are disposed a plurality of boards 24, 25 such as a power supply board 24 to supply power to the light source lamps 11 stored in the carriage 10, a control board 25 to control the carriage motor and control reading of the photoelectric sensor 13 of the sensor board 19, and an image processing board (the board shown in the figure is integrally formed on the board 25) to process data from the sensor board 19 mounted on the carriage 10.

The power supply board 24 supplies power to a configuration unit required for image reading. Therefore, although not shown in the figure, the board is provided with an input power supply terminal and output power supply terminal. Then, on the board are mounted relatively tall lead insertion type (THD: Through Hole Mount Device) circuit devices such as a transformer, capacitor, transistor and diode. Various kinds of power supply from the output terminal are supplied to electric devices via the control board 25 described later. In the apparatus shown in the figure, the power supply board 24 supplies power to the light source lamps 11 mounted on the carriage 10 and carriage motor (not shown).

The control board 25 transmits a control signal required for image reading to the circuit devices. Concurrently therewith, the board 25 issues a signal to control image reading in the photoelectric sensor 13. Further, the board 25 receives an output signal from the photoelectric sensor 13. An image reading signal transferred from the photoelectric sensor 13 is provided with digital signal conversion and output data correction in a processing circuit disposed on the control board 25, and is transferred to outside the apparatus via an interface circuit.

[Board Layout Structure]

As shown in FIG. 3, the power supply board 24 and control board 25 are attached to the board placement area Br of the board storage section 5 inside the casing 1. The attachment structure will be described according to FIGS. 6 and 7. The board storage section 5 is housing-formed as the board placement area Br inside the casing 1. This housing (second housing Br) is comprised of the area enclosed with the top 5 a, bottom plate Bs, barrier wall 23 and the side wall 1 r on the rear side.

On the other hand, the circuit boards are comprised of different separate boards, power supply board 24 and control board 25. Then, both of the boards 24, 25 are disposed at a distance vertically in the layered state, the power supply board 24 is disposed in the upper portion, and the control board 25 is disposed in the lower portion.

The control board 25 (hereinafter, referred to as first board) in the lower portion is fixed to an installation foot portion 25 s (first board support member) formed on the bottom plate Bs of the casing 1. Further, the power supply board 24 (hereinafter, referred to as second board) in the upper portion is fixed at its one end portion to a bracket 44 fixed to a casing side wall, while being fixed at its other end to an installation foot portion 24 s (second board support member) formed in a casing wall portion.

At this point, in a state in which a second blast fan 43 is attached, the bracket 44 is provided with air vents 36 so that an air blast from the fan is sent to between the first board 24 and a partition plate 45 (see FIG. 8). In FIG. 8, the air vent is shown by a circular shape, and such a shape may also be adopted that attachment portions at opposite ends of the second blast fan 43 to attach the second blast fan 43 to the bracket 44 are left, and that an opening is formed between the portions.

Then, the partition plate 45 is disposed between the first board 24 and the second board 25 to partition vertically. The partition plate 45 is formed of a material (for example, metal plate) with thermal conductivity higher than that of the circuit boards (first board and second board).

In between the first board 24 and the second board 25, a gap Ga between the top 5 a and the first board 24 is formed to be wider than a gap Gb between the first board 24 and the partition plate 45 and a gap Gc between the partition plate 45 and the second board 25. Further, the gap Gc is formed to be wider than the gap Gb. Accordingly, the gap Ga is formed in the relationship of gap Ga>gap Gc>gap Gb.

Then, the second blast path 40 and second blast fan 43 are disposed at end portions of the first board 24 disposed in the upper portion and the second board 25. In the outside air sent from the second blast fan 43, a first air flow Af1 (first blast path) is formed between the top 5 a and the first board frontside, a second air flow Af2 (second blast path) is formed between the first board backside and the partition plate 45, and a third air flow Af3 (third blast path) is formed between the partition plate backside and the second board frontside. Then, the air from each path is released to the outside from the air outlet 9.

It is set that an air volume of the first air flow Af1 is higher than an air volume of the second air flow Af2, and that an air volume of the third air flow Af3 is lower than the air volume of the first air flow Af1 and is higher than the air volume of the second air flow Af2 (see FIG. 7). The air volume adjustments in this case are made with an area ratio of air flow directions from the blast fan 43 toward the gap Ga, Gap Gb and gap Gc.

In such a configuration, the first air flow Af1 sends heat generated from the first board frontside in the direction from the air vent 8 to the air outlet 9. Concurrently therewith, the heat of the first board frontside undergoes convection inside the gap Ga (space with the wide gap). Further, the second air flow Af2 is sent smoothly to the air outlet 9 as a laminar flow without being a turbulent flow between the first board backside and the partition plate 45.

In other words, since lead insertion type parts such as a transformer, capacitor and IC chip which are relatively tall parts are arranged on the board frontside, a turbulent flow is made and heat is disrupted. In contrast thereto, since relatively short surface package type parts are packaged on the board backside, the air sent from the second blast fan 43 maintains a state of the laminar flow, and discharges heat of the board smoothly from the air outlet 9.

[Transmission Cable]

The transmission cable 26 connects between the carriage 10 and the control board 25. The transmission cable 26 is comprised of a flat cable formed of a power supply line 26 a to supply power to the light source lamps 11, and a plurality of control lines 26 b such as a data line to transmit image data read with the photoelectric sensor 13, and control data lines to control lamp flashing and photoelectric conversion. The transmission cable 26 shown in the figure is formed of a flexible cable that becomes deformed in association with a shift of the carriage 10.

[Cooling Mechanism]

A cooling mechanism inside the casing 1 will be described with reference to FIG. 5. As described according to FIG. 3, the first blast path 30 is formed between the first air vent 7 and the carriage travel area (first housing) Cr formed in the casing 1, and the second blast path 40 is formed between the second air vent 8 and the board placement area (second housing) Br.

The air vents 7 and 8 described previously are disposed in the rear-side side wall 1 r (or, front-side external wall 1 f, right-side wall 1 s, left-side wall 1 n) of the casing 1 close to a home position of the carriage 10. In other words, the first air vent 7 is disposed in a reading start position Hp of the carriage 10 for performing scanning operation, and the first blast path 30 is disposed in the main scanning direction (Ax direction in FIG. 3) so that cooling air is sent from the air vent 7 to the carriage 10 at rest. Further, the cooling air sent from the first blast path 30 is sent to the entire carriage travel area (first housing) Cr.

The first blast path 30 is comprised of a filter cover 31 coupled to the first air vent 7, a first air filter 32 stored in the cover, and a vent (not shown) of the barrier wall 23. In other words, the path is comprised of a path for guiding outside air from the first air vent 7 to the carriage travel area (first housing) Cr through the first air filter 32.

The filter cover 31 is integrally formed, while protruding from the inner wall of the rear-side side wall 1 r inwardly in the shape of a hood, and incorporates the first air filter 32 thereinto. The air filter 32 is made of (porous material such as, for example, polyurethane resin and polyester resin), and a collection amount η1 of dust thereof is obtained by the following equation. η=(1−Wp/Wf)×100[%]  (Eq.1) η: Collection efficiency; Wf: Amount of supplied dust [g]; Amount of dust collected with the filter [g]

As shown in FIG. 5, the filter cover 31, and next, the first blast fan 33 are arranged in the main scanning direction from the rear-side side wall 1 r. The first air filter 32 (in the filter shown in the figure, filter 32 a and filter 32 b) is incorporated into the filter cover 31. In the first blast fan 33, the fan is attached to a rotating shaft bearing-supported on a unit frame, and the rotating shaft is equipped with a fan motor (not shown) provided with a reduction mechanism.

The structure of the first air filter 32 is comprised of a three-layer structure having an air layer between the filters 32 a and 32 b. Then, the collection efficiency (η1) obtained by the above-mentioned (Eq.1) is set at a value higher (larger) than that of a second air filter 42 of the second blast path 40, described later.

The second blast path 40 is comprised of a filter cover 41 coupled to the second air vent 8, and the second air filter 42 stored in the cover. Then, the path is comprised of a path for guiding outside air from the second air vent 8 in the sub-scanning direction through the second air filter 42. The second blast fan 43 is disposed in the second blast path 40, and in the blast fan 43, the fan is attached to a rotating shaft bearing-supported on the unit frame, and the rotating shaft is equipped with a fan motor (not shown) provided with a reduction mechanism.

The second blast fan 43 blows air in the sub-scanning direction (Ay), and sends cooling air to the board placement area (second housing) Br. The collection efficiency (η2) of the second air filter 42 is obtained by (Eq.1) as described previously, and the collection efficiency (η1) of the first air filter 32 and the collection efficiency (η2) of the second air filter 42 are set at [η1>η2].

For collection efficiencies of the first and second filters 32 and 42, “mesh roughness” is configured to be dense, or the effective filtering volume is set to be high. In the filters shown in the figure, the mesh roughness and filter volume of the first air filter 32 is set to be higher than in the second air filter 42. In other words, the first air filter 32 is comprised of two filters with the mesh roughness being dense. In contrast thereto, the second air filter 42 is comprised of a single filter with the mesh roughness being rough.

[Blast Volume Regulation]

The first air vent 7 and second air vent 8 are comprised of apertures for regulating a volume of air introduced to inside the casing 1. A plurality of vent holes 7 a in the shape of a grill is formed in the rear-side side wall 1 r of the casing 1, and as the total area (Area) of the vent holes, the first air vent 7 is set for an area larger than that of the second air vent 8 (Area 7>Area 8).

Then, a blast volume by the first air vent 7 and first blast fan 33 is set to be higher than a blast volume by the second air vent 8 and second blast fan 43. For example, when the area of vent holes of the first air vent 7 is a times the area of vent holes of the second air vent 8, the air volume of the first blast path 30 is a times the air volume of the second blast path 40 (in this case, the capacity of the blast fan is not considered).

From the above-mentioned configuration, the cooling air sent from the first blast path 30 to the carriage travel area (first housing) Cr is higher in the clean degree and concurrently higher in the air volume than those of the cooling air of the second blast path 40. In contrast thereto, the cooling air of the second blast path 40 sent to the board placement area (second housing) Br is lower in the clean degree and smaller in the air volume than those of the cooling air of the first blast path 30.

Accordingly, even when the light source lamps 11 mounted on the carriage 10 become high temperatures, the lamps are cooled by an air volume of high capacity, and concurrently, it is possible to reduce the dust amount adhering to imaging optical parts such as the mirrors 17 and condenser lens 18 mounted on the carriage 10. On the other hand, for the circuit boards (power supply board, control board and the like) with relatively low heating values as compared with the light source lamp and the like, the air volume is set to be low, the clean degree is also set to be low, and therefore, it is possible to reduce the load of the fan motor required for sending air.

This application claims priority from Japanese Patent Application No. 2014-262017 filed on Dec. 25, 2014 in Japan incorporated herein by reference. 

The invention claimed is:
 1. An image reading apparatus having a blast mechanism for sending cooling air to inside a casing of the image reading apparatus, the blast mechanism comprising: first and second boards disposed in a vertical direction inside the casing, a partition plate disposed between the first board and the second board, and a blast fan for sending cooling air to the first and second boards, wherein a top of the casing, the first board, the partition plate and the second board are disposed in this order from above, while being spaced a distance apart, a first blast path is formed between the top and the first board, a second blast path is formed between the first board and the partition plate, a third blast path is formed between the partition plate and the second board, and the blast fan is disposed in a position overlapping each blast path when viewed from a direction intersecting the vertical direction.
 2. The image reading apparatus according to claim 1, wherein the partition plate is formed of a material with thermal conductivity higher than that of the first board.
 3. The image reading apparatus according to claim 1, wherein the first board is formed with a power supply circuit for supplying power to a light source lamp disposed inside the casing, and the second board is formed with a control circuit of an image reading section disposed inside the casing.
 4. The image reading apparatus according to claim 1, wherein the casing houses a placement platen for placing an image to be read, a reading carriage for reading the image, a light source lamp mounted on the reading carriage, a power supply board for controlling supply of power to the light source lamp, and a control board for controlling reading operation of the reading carriage, and the power supply board forms the first board, while the control board forms the second board.
 5. An image reading apparatus having a blast mechanism for sending cooling air to an inside of a casing of the image reading apparatus, the blast mechanism comprising: first and second boards disposed vertically inside the casing, a partition plate disposed between the first board and the second board, and a blast fan for sending cooling air to the first and second boards, wherein a top of the casing, the first board, the partition plate and the second board are disposed in this order from above, while being spaced a distance apart, a first blast path is formed between the top and the first board, a second blast path is formed between the first board and the partition plate, a third blast path is formed between the partition plate and the second board, the blast fan is disposed in a position for forming a flow of cooling air in each blast path, a gap between the top and the first board is set wider than a gap between the first board and the partition plate, and an air volume of the first blast path is set at a capacity higher than an air volume of the second blast path.
 6. An image reading apparatus having a blast mechanism for sending cooling air to an inside of a casing of the image reading apparatus, the blast mechanism comprising: first and second boards disposed vertically inside the casing, a partition plate disposed between the first board and the second board, and a blast fan for sending cooling air to the first and second boards, wherein a top of the casing, the first board, the partition plate and the second board are disposed in this order from above, while being spaced a distance apart, a first blast path is formed between the top and the first board, a second blast path is formed between the first board and the partition plate, a third blast path is formed between the partition plate and the second board, the blast fan is disposed in a position for forming a flow of cooling air in each blast path, the blast fan is attached to a bracket fixed to the casing, and the partition plate is integrally coupled to the bracket, and a vent hole for allowing the cooling air from the blast fan to pass through is formed in the bracket. 